Dollars are more relevant because units can have more or less relative value depending on what dollar amount they're associated with. For example, two card counters compare their results in terms of units won per hours played. Both players spread 1-16 units, but player A is a nickel player and player B is a black chip player. Their unit results will differ wildly because of game quality/availability, number of hands played, heat, and so on. Units are a good way to focus on proper strategy and bankroll management, but not all units are created equal!